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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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90                                   ALASKAN GLACIER STUDIES
1905 and by the extent of healing of the glacier in that year, the entire Galiano Glacier from its valley head to the periphery of its buried piedmont bulb was under the influence of a spasmodic advance, which broke the surface of the glacier and pushed up through the alluvial fan as well as the area of morainic hillocks beyond it, at the same time destroying the alluvial fan, overturning the forest that grew on the glacier and that which was growing to the south of the alluvial fan. Ablation on the deeply moraine-covered ice soon hid the crevasses, partly by melting down of the surface, but largely by the sliding of the moraine into the crevasses, so that in 1905 the glacier surface showed no signs of the pronounced breakage of a few years before, which would be recognized by an observer unfamiliar with the phenomenon. This latter point would perhaps seem improbable were it not for the evidence that the advancing glaciers of 1906 furnish concerning the rapidity with which such a broken surface is healed by ablation.
Now the glacier is returning to its former condition and the evidence of it was especially seen along the sides in 1909 where marginal drainage was again developing, and in doing so revealing some of the crevasses that were formed during the advance and that since then had been hidden by the ablation moraine. It was also shown by the immaturity of the ice drainage. The return of stagnation has again permitted the encroachment of vegetation upon the glacier, and it is rapidly spreading and developing alder thickets; but the presence of buried crevasses beneath the moraine, and the necessity of development of drainage, are causing so much slumping that the advance of the vegetation is interrupted here and there.
Changes were also in progress on the outer area of stagnant, buried ice, but this had not yet proceeded far and the morainic hillocks still rose prominently above the surface. However, vegetation was taking root here also, alluviation was in progress between the hillocks, and probably the surface of the moraines was being lowered by the melting of the buried ice. There was a tendency toward the return of the condition of 1890, but it will be many years before this work is complete, for there were many irregularities to be removed or graded up before an even-surfaced alluvial fan is again built here; and, although glacial streams bore great quantities of sediment, and were relatively rapid agencies of deposition, there was a large area to be covered and much deposit was necessary. At the observed rate of change it is probable that a quarter of a century hence the signs of the spasmodic breaking of the Galiano Glacier will still be visible here, while in the valley portion and its small inner piedmont bulb all signs of the advance will have disappeared. Ablation on the glacier itself is far more rapid than on the outer bulb which bears so thick a coat of morainic debris and alluvial fan gravels that no ice has been observed in it.
In 1910 and 1913 the Galiano Glacier seemed, from the bay, to be essentially as in 1909, except for the increased covering of vegetation.
BLACK GLACTBH
Black Glacier, a little over a mile east of Galiano Glacier (Map 2) resembles the Galiano in several respects, though in others the two glaciers are quite different. Although shorter and narrower than the Galiano, the Black Glacier occupies a similar steep-sided, short valley and is supplied with ice by several steeply-descending cascading tributaries at the valley head. Its surface to a point far up in the mountain valley is covered with, ablation moraine, and in the lower portion, in the areas of deepest moraine, there is considerable alder growth, forming small thickets. There is no continuous alder thicket,